HT Subwoofer Impedance

O

Openupshop

Audiophyte
I have Def Tech Powerfield 10" Subwoofer that works great. I couldn't find the impedance online and the manual I found for it online, doesn't list it. So I took it out of the enclosure and measured it with a multimeter & it reads 110. Am I missing something here? Isnt't supposed to be 2, 4, 6 or 8 ohms?? Why the crazy reading

I found an old listing from years ago, of the same Subwoofer, but the 8" version listed online as part of a HT in a box. The speakers in that set are the Procinema 60's & have a 4 ohm impedance listing, the Sub again has no impedance listed.
ProCinema HT

Anyone have the same sub or know why as to the impedance reading?
 
XEagleDriver

XEagleDriver

Audioholic Chief
I have Def Tech Powerfield 10" Subwoofer that works great. I couldn't find the impedance online and the manual I found for it online, doesn't list it. So I took it out of the enclosure and measured it with a multimeter & it reads 110. Am I missing something here? Isnt't supposed to be 2, 4, 6 or 8 ohms?? Why the crazy reading
Reading is not crazy, the DT sub is a powered subwoofer, NOT a passive speaker.

The 2, 4, 6, 8 ohms you refer to are typical values for passive speakers.

Cheers,
XEagleDriver


Sent from my SM-G975U using Tapatalk
 
O

Openupshop

Audiophyte
Reading is not crazy, the DT sub is a powered subwoofer, NOT a passive speaker.

The 2, 4, 6, 8 ohms you refer to are typical values for passive speakers.

Cheers,
XEagleDriver


Sent from my SM-G975U using Tapatalk
Just to be clear, I took the driver out of its enclosure and disconnected the line which connected it to the plate amp. And then took the reading. I say this because with my other powered sub, when I disconnect the driver and measure, I get a 3.9 ohm reading, which makes sense since its a 4 ohm sub. As they are both powered subs, can you elaborate on the diff please. Much thanks.
 
lovinthehd

lovinthehd

Audioholic Jedi
Maybe its your multimeter? What multimeter/settings are you using? Why are you wanting to measure the dc resistance (RE) particularly? Altho it is generally less than t than its impedance that will vary with frequency in actual use....

ps Just saw you apparently successfully measured a different driver.. Planning on changing amps or something?
 
XEagleDriver

XEagleDriver

Audioholic Chief
Just to be clear, I took the driver out of its enclosure and disconnected the line which connected it to the plate amp. And then took the reading. I say this because with my other powered sub, when I disconnect the driver and measure, I get a 3.9 ohm reading, which makes sense since its a 4 ohm sub. As they are both powered subs, can you elaborate on the diff please. Much thanks.
Copy, that makes the original question more understandable (at least to me LOL).

For a passive speaker, the impedance is measured at the terminals and therefore is influenced by the crossover and speakers themselves in concert.
Impedance is not a static value, it varies with frequency.
The marketing convention of providing one "value" is a crude attempt to convey how easy or difficult the speaker system is to drive (many times this value is skewed towards sale volume vice accuracy).

I do not know, but believe, the 3.9 ohm reading on a "4 ohm" powered sub (not sure what that means exactly) is more likely coincidental than illuminating.

Is the sub in question having a problem? If so, the much higher 110 ohm reading could indicate that.
Or is this more of an academic/interest inquiry?

Sent from my SM-G975U using Tapatalk
 
lovinthehd

lovinthehd

Audioholic Jedi
Copy, that makes the original question more understandable (at least to me LOL).

For a passive speaker, the impedance is measured at the terminals and therefore is influenced by the crossover and speakers themselves in concert.
Impedance is not a static value, it varies with frequency.
The marketing convention of providing one "value" is a crude attempt to convey how easy or difficult the speaker system is to drive (many times this value is skewed towards sale volume vice accuracy).

I do not know, but believe, the 3.9 ohm reading on a "4 ohm" powered sub (not sure what that means exactly) is more likely coincidental than illuminating.

Is the sub in question having a problem? If so, the much higher 110 ohm reading could indicate that.
Or is this more of an academic/interest inquiry?

Sent from my SM-G975U using Tapatalk
He's measuring dc resistance (I think) of the driver's voice coil it seems (T/S parameter Re). Generally that will be a bit below the area it will range in actual use, and that range does variy by frequency. You can do that with a driver, but a complete speaker not so much as the crossover will interfere IIRC.
 
TLS Guy

TLS Guy

Audioholic Slumlord
I have Def Tech Powerfield 10" Subwoofer that works great. I couldn't find the impedance online and the manual I found for it online, doesn't list it. So I took it out of the enclosure and measured it with a multimeter & it reads 110. Am I missing something here? Isnt't supposed to be 2, 4, 6 or 8 ohms?? Why the crazy reading

I found an old listing from years ago, of the same Subwoofer, but the 8" version listed online as part of a HT in a box. The speakers in that set are the Procinema 60's & have a 4 ohm impedance listing, the Sub again has no impedance listed.
ProCinema HT

Anyone have the same sub or know why as to the impedance reading?
You must have made an error in your reading. If it works, it is not 110 ohms, or the output voltage of the amp would have to be crazy, unless it is a high impedance driver and the sub amp contains a transformer. That would be a system akin to some 70 volt PA systems. I suspect though the terminals have a layer of oxidation. Take a rat tailed file and make the speaker terminals shiny again, and remeasure.

The bottom line is that if that sub works from the line it is driven by from the receiver, and when you plug that exact same plug into the other sub, and you get no sound, then that amp is bad.

I really think you want to be careful taking working equipment apart for no good reason. You had no good reason to do what you did. That sort of endeavor often results in ruining perfectly good working units, that would be working if you had not taken them apart.
 
O

Openupshop

Audiophyte
This Sub itself works flawlessly, just as good as I remember it ever.

That being said, its definitely not the multimeter, I put in a new battery. Somehow I ended up with 4 sets of multimeter probes, so I tried different probes for the multimeter as well. I tested a bunch of other items for which I am certain of the expected readings, i.e. vape coils, computer parts, and multimeter performed perfectly. I couldn't take a photo of both the driver and with me having probes on them, but see below for pics(cropped it to lessen file size per forum image size limits). I literally took the readings over ten times and different points of the contacts. I even measured touching the tensils that run up to the terminals, as well as right behind the terminals. All reading gives me 111 or 110. Lastly, I have scratcher tool for something else, I used it to take a bit off the terminals in case it is oxidation or just dirty, but again same reading afterwards.

I then went around and checked a bunch of others, they all read 3.5 to 3.9 which makes sense from what ive read that whenever its listed as 4 ohms, it will read a bit below, which was lovinthehd above also noted.

This is an old sub, and couple of times I put up on ebay for a few weeks, twice someone asked me what the impedance was & I tried to look it up all over the web without success. Perhaps the fact that the manual and old sales postings don't list the impedance in the specs, means its something like what TLS Guy... "...high impedance driver"

I found another Def Tech driver that looks identical but is a 15 inch version on ebay & the impedance is listed as 75 ohms for it HERE


2.JPG

1.JPG
 
TLS Guy

TLS Guy

Audioholic Slumlord
This Sub itself works flawlessly, just as good as I remember it ever.

That being said, its definitely not the multimeter, I put in a new battery. Somehow I ended up with 4 sets of multimeter probes, so I tried different probes for the multimeter as well. I tested a bunch of other items for which I am certain of the expected readings, i.e. vape coils, computer parts, and multimeter performed perfectly. I couldn't take a photo of both the driver and with me having probes on them, but see below for pics(cropped it to lessen file size per forum image size limits). I literally took the readings over ten times and different points of the contacts. I even measured touching the tensils that run up to the terminals, as well as right behind the terminals. All reading gives me 111 or 110. Lastly, I have scratcher tool for something else, I used it to take a bit off the terminals in case it is oxidation or just dirty, but again same reading afterwards.

I then went around and checked a bunch of others, they all read 3.5 to 3.9 which makes sense from what ive read that whenever its listed as 4 ohms, it will read a bit below, which was lovinthehd above also noted.

This is an old sub, and couple of times I put up on ebay for a few weeks, twice someone asked me what the impedance was & I tried to look it up all over the web without success. Perhaps the fact that the manual and old sales postings don't list the impedance in the specs, means its something like what TLS Guy... "...high impedance driver"

I found another Def Tech driver that looks identical but is a 15 inch version on ebay & the impedance is listed as 75 ohms for it HERE


View attachment 48950
View attachment 48951
I believe you. That is a high impedance driver. No idea what really drove that decision. I will file that in my memory banks, as if we get a post wanting to turn one of those passive, or replace the plate amp with a generic one, they would be out of luck. In addition if someone did happen to touch those speaker terminals when it was operating, they would get a very nasty electric shock, they would not have predicted.
 
Z

ZenLunatic

Audiophyte
I have Def Tech Powerfield 10" Subwoofer that works great. I couldn't find the impedance online and the manual I found for it online, doesn't list it. So I took it out of the enclosure and measured it with a multimeter & it reads 110. Am I missing something here? Isnt't supposed to be 2, 4, 6 or 8 ohms?? Why the crazy reading

I found an old listing from years ago, of the same Subwoofer, but the 8" version listed online as part of a HT in a box. The speakers in that set are the Procinema 60's & have a 4 ohm impedance listing, the Sub again has no impedance listed.
ProCinema HT

Anyone have the same sub or know why as to the impedance reading?
I have wondered the same thing multiple times. I just came across this table showing the impedance of a bunch of models of def tech subs. Hope this helps others out there looking for this info:
844EE235-B7E0-4578-8C4B-14F18DBE4807.jpeg
 
TLS Guy

TLS Guy

Audioholic Slumlord
I have wondered the same thing multiple times. I just came across this table showing the impedance of a bunch of models of def tech subs. Hope this helps others out there looking for this info:View attachment 52123
We have had this before. If you build design a powered subwoofer, you design the amp and driver as a unit. You can make the driver any impedance you want. By the way, the actual impedance is actually a little higher than the measured DC resistance. You measure impedance dynamically with a woofer tester connected to a computer. You can order one from Parts Express.
 
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